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Invisibility cloaks built from 'off-the-shelf materials'

The creation of invisibility cloaks has always been considered very much on the cutting edge of physics and technology, treading the line between science, science fiction and pure magic.

But while many researchers beaver away in labs playing around with complex nanotechnology and light refraction techniques, physicists Joseph Choi and John Howell from the University of Rochester in the US have figured out a way to build an invisibility cloak using off-the-shelf materials. And the good news is that they're not even that expensive. "There have been many high-tech approaches to cloaking and the basic idea behind these is to take light and have it pass around something as if it isn't there, often using high-tech or exotic materials," explains Howell in a University of Rochester video. "We just figured a very simple of doing that would be using standard lenses and things we would normally find in the lab."

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So what would you need if you decided to attempt to make an invisibility cloak yourself? According to a paper by Choi and Howell, all you would need to invest in some isotropic, off-the-shelf optics. To be precise, you would need four lenses called achromatic doublets. These can be purchased from specialist optics retailers are commonly used in imaging and physics for applications including colour correction and focussing laser beams. They don't even need to be too large, as the model is scalable and the lenses are capable of bending light no matter what their size.

To design a working invisibility cloak, there are several things you have to keep in mind. Firstly you need to make sure that it can cope with the fact that the world works in three dimensions, meaning that if the cloak or the viewer moves, the illusion must be maintained. It's not enough for the cloak to work if the viewer is only standing straight-on to it. Secondly, it is all very well to hide the object under the cloak, but to maintain the illusion, the background cannot be distorted by it.

Choi and Howell claim to overcome both of these problems with their combination of lenses in what Choi describes as "simplified version of a perfect cloaking device". His definition of "perfect" is that it can do three-dimensional, continuous, multi-directional cloaking, no matter what direction the rays of light are coming from. "Perfect" does not yet mean a Harry Potter-style sheet of material that one could slip over oneself at any given moment, but at least we know the technology now exists to make the magic happen.